Halogenated derivatives of aliphatic acids and method of making same



Patented June 19, 1951 UNITED STAT TENT OFFICE HALOGENATED DERIVATIVES OF ALI- PHATIC ACIDS AND METHOD OF MAKING SAME No Drawing. Original application November 7,

1945, Serial No. 708,462.

Divided and this application September 25, 1947, Serial No. 776,150

7 Claims. 1

carbon atoms in a chain of the acyl radical to form a corresponding a1pha-gamma-dihalcaliphatic carboxylic acid which is thermally unstable and may be dehydrohalogenated by heating to produce an alpha-halo -lactone of the gamma-hydroxy carboxylic acid as an ultimate product. The alpha-halo-gamma-lactones thus produced are useful as chemical agents for the preparation of a Wide variety of more complex derivatives of the aliphatic carboxylic acid. They are particularly useful as intermediate agents in a method for the production of methionine and its homologues.

Any lactone of a saturated gamma-hydroxyaliphatic monocarboxylic acid may be used as a starting material in the process. Examples of such starting materials are the lactones of gamma-hydroxy-butyric acid, gamma-hydroxyvaleric acid, gamma-hydroxy-isovaleric acid, gammahydroXy-caproic acid, etc. The lactone of gamma-hydroxy-butyric acid is readily available as a by-product from the destructive distillation of Wood, and the alpha-halo derivatives of this lactone are useful as intermediates in the synthesis of methionine itself. For these reasons the lactone of gamma-hydroXy-butyric acid is a preferred starting material.

The lactones may be halogenated by passing a halogen, e. g. chlorine or bromine, into the same while heating the mixture at a temperature sufiicient to cause fairly rapid reaction. The halogenation occurs most readily and rapidly when carried out in the presence of a substance capable of forming an addition compound With an acyl halide, e. g. acetyl chloride. Examples of substances having this property and useful as catalysts for the halogenation are phosphorus trichloride, phosphorus pentachloride, phosphorus tribromide, aluminum chloride, ferric chloride, etc. The phosphorus halides are particularly effective for the purpose and are preferred. Only a minor amount, e. g. 0.02 molecular equivalent, or less, of a phosphorus halide is required per mole of thelactone reactant in order to obtain halogenation at a rapid rate. The halogenation is usually carried out at temperatures in the order of from to 150 C., but it may be accomplished at lower, or somewhat higher, temperatures if desired. The halogen apparently adds directly to the molecule of the lactone with formation of an alphagarnma-dihalo-aliphatic carboxylic acid. Only a minor amount of hydrogen halide is evolved.

The alpha gamma dihalo carboxylic acids thus produced are thermally unstable compounds which undergo dehydrohalogenation and lactone formation at temperatures below their boiling temperatures at atmospheric pressure. In some instances, they may be distilled under vacuum to collect a substantial portion thereof in undecom posed form. The alpha-gamma-dihalo-carbox ylic acids may be esterified by reaction with alcohols such as methyl, ethyl, or propyl alcohol, etc, the esters may readily be separated and purified, e. g. by distillation. The alpha-gamma-dihaloalphatic monocarboxylic acids are new co1npounds which are useful as chemical agents in forming a wide variety of more complex derivatives of the aliphatic carboxylic acids parent thereto. For instance, one or both of the halogen atoms thereof may be displaced by reaction of such compound, or an ester thereof, with an alkali salt of a carboxylic acid so as to form a complex polyester. The alpha-gamma-dihalo-carboxylic acids have the general formula:

wherein each X represents a halogen atom, e. g.

chlorine or bromine, and R represents hydrogen or an alkyl radical.

An alpha-gamma-dihalo-aliphatic carboxylic acid prepared as described above is readily dehydrohalogenated to form a corresponding alphahalo-gamma lactone by heating the same to a temperature at which hydrogen halide is evolved. The dehydrohalogenation action usually occurs rapidly upon heating the dihalo compound at temperatures in the order of from to C. at sub-atmospheric pressure. Higher temperatures may in some instances be required, particularly when the decomposition is carried out at atmospheric pressure. The alpha-halolactone product is readily purified by distillation.

The following examples described certain ways in which the invention has been practiced, but are not to be construed as limiting the scope of the invention.

Example 1 A solution of 71 grams of phosphorus tribromide and 1120 grams of gamma-butyrolactone was heated to a temperature of 100 C., and 1975 grams of bromine were added gradually and with stirring. The bromine was added at a rate of about 1 gram per second over a period of about 2.5 hours, after which the rate of bromine addition was reduced somewhat in order to avoid vaporization of free bromine from the mixture. Considerable heat was evolved during the bromination reaction which was carried out for the most part at temperatures of between 120 and 130 C. After addin the bromine, the mixture was heated at 130 C. for a period of 4 hours in order to assure substantial completion of the reaction. The crude brominated product weighed 3100 grams and consisted for the most part of alpha-gamma-dibromo-butyric acid. The yield of the crude acid was approximately 98 per cent of theoretical. The alpha-gamma-dibromobutyric acid was heated under vacuum, first to evolve the hydrogen bromide formed by thermal decomposition of the dibromo-butyric acid, and thereafter to distill the resultant alpha-bromobutyrolactone product. The alpha-bromo-gamma-butyrolactone is a colorles liquid which boils at from 94 to 106 C. at 1 millimeter absolute pressure, has a density at 25 C. of 1.79, and has an index of refraction, n of 1.509. The yield of alpha-bromo-gamma-butyrolactone was 85 per cent of theoretical, based on the gamma butyrolactone starting material.

Example 2 By procedure similar to that described in Example 1, chlorine was reacted with butyrolactone in the presence of phosphorus trichloride as a catalyst to form alpha-gamma-dichloro-butyric acid, and the latter was subjected to distillation under vacuum. In this instance, a portion of the dihalo-butyric acid was decomposed to form alpha-chloro-butyrolactone, which was collected as a fraction of distillate, and another portion distilled without decomposition and was recovered as the purified compound. The alphagamma-dichloro--butyric acid is a colorless liquid which distills at temperatures of from 112 to 114 C. at 4 millimeters absolute pressure, has a density at 25 C. of 1.404, and has an index of refraction, 7LD25, of 1.477. The alpha-chloro-gamma-butyrolactone is also a colorless liquid. It distills at 98 to 100 C. at 4 millimeters absolute pressure, has a density at 25 C. of 1.361, and has an index of refraction, 121%, of 1.469.

Example 3 Approximately 192 grams of bromine was added in dropwise manner and with stirring to a solution of 1 cubic centimeter of phosphorus tribromide in 125 grams of gamma-valerolactone while heating the mixture at temperatures of from 95 to 100 C. The bromine was added over a period of 3 hours, after which heating of the mixture at the temperatures just mentioned was continued for another 3 hours. The alpha-gammadibromo-valeric acid, thus formed, was heated under vacuum, first to evolve hydrogen bromide formed due to thermal decomposition of the same, and thereafter to distill the alpha-promogamma-valerolactone product. The alphabromo-gamma-valerolactone is a colorless liquid which boils at approximately 120 to 125 C. at

4 7 millimeters absolute pressure. It has a density at 25 C. of 1.595 and an index of refraction, 1111 of 1.4905. The yield thereof was approximately 71 per cent of theoretical, based on the amount of valerolactone consumed in the initial bromination reaction.

This application is a division of our copending application, Serial No. 708,462, filed November 7, 1946, now patent No. 2,530,348.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the method or compounds herein disclosed, provided the steps or compounds stated by any of the followin claims or the equivalent of such steps or compounds be employed.

We therefore particularly point out and dis tinctly claim as our invention:

1. The method which comprises reactin an elemental halogen of the clas consisting of chlorine and bromine with a lactone of a gammahydroxy-aliphatic monocarboxylic acid by pass-- ing the halogen into the lactone while heating the mixture at a reaction temperature below the decomposition temperature of the alpha, gammadihalo-carboxylic acid reaction product.

2. The method which comprises formin an aliphatic alpha, gamma-dihalo-monocarboxylic acid by reacting an elemental halogen of the class consisting of chlorine and bromine with a lactone of a gamma-hydroxy-aliphatic monocarboxylic acid at about atmospheric pressure and a reaction temperature between and C.

3. The method which comprises forming an aliphatic alpha, gamma-dihalo-monocarboxylic acid by passing an elemental halogen of the class consistin of chlorine and bromine into a solution of a major amount of a lactone of a gammahydroXy-aliphatic monocarhoxylic acid and a catalytic amount of a substance capable of forming an addition compound with acetyl chloride while heating the mixture at about atmospheric pressure to a reaction temperature between 80 and 150 C.

4. The method which comprises forming an aliphatic alpha, gamma-dihalo-inonocarboxylic acid by passing an elemental halogen of the class consisting of chlorine and bromine into a solution of a major amount of a lactone of a gamma-hydroxy-aliphatic monocarboxylic acid and a catalytic amount of a phosphorus halide while heating the mixture at about atmospheric pressure to a reaction temperature between 80 and 150 C.

5. The method which comprises forming alpha, gamma-dibromobutyric acid by passing bromine into a solution of a major amount of the lactone of gamma-hydroxy-butyric acid and a catalytic amount of a phosphorus bromide while heating the mixture at about atmospheric pressure to a reaction temperature between 80 and 150 C.

6. The method which comprises forming alpha, gamma-dichlorobutyric acid by passing chlorine into a solution of a major amount of the lactone of gamma-hydroxy-butyric acid and a catalytic amount of a phorphorus chloride while heating the mixture at about atmospheric pressure to a reaction temperature between 80 and 150 C.

7. The method which comprise forming alpha, gamma-dibromovaleric acid by passing bromine into a solution of a major amount of the lactone of gamma-hydroxy valeric acid and a catalytic amount of a phosphorus bromide while heating the mixture at about atmospheric pressure to a reaction temperature between 80 and OTHER REFERENCES 150 C. Wohlgemuth et a1: Comptes Rendus, vol. 158,

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17, p. 251 (1933). file of this patent Venus-Danilova et a1.: Chem. Abst., v01. 33,

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2,411,875 Gresham et a1. Dec. 3, 1946 Simons: Ind. Eng. Chem., Vol. 39, page 238 

1. THE METHOD WHICH COMPRISES REACTING AN ELEMENTAL HALOGEN OF THE CLASS CONSISTING OF CHLORINE AND BROMINE WITH A LACTONE OF A GAMMAHYDROXY-ALIPHATIC MONOCARBOXYLIC ACID BY PASSING THE HALOGEN INTO THE LACTONE WHILE HEATING THE MIXTURE AT A REACTION TEMPERATURE BELOW THE DECOMPOSITION TEMPERATURE OF THE ALPHA, GAMMADIHALO-CARBOXYLIC ACID REACTION PRODUCT. 